Silver alloy



Patented Aug. 14, 1934 UNITED STATES PATENT? OFFICE SILVER ALLOY EdwardF. Kern, New York, N. Y., assignor to- The American Metal Company,Limited, New York, N. Y., a corporation of New York No Drawing.Application May 8, 1931, Serial No. 536,087

5 Claims.

This invention relates to the production of tarnish-resisting silveralloys of a fineness equivalent to sterling 925 and standard quality 900fine, as well as the composition of other'silver alloys possessingtarnish-resisting properties.

It is well-known that silver alloys and articles made of silver whenexposed to the atmosphere or when in contact with substances containingsulfur assume a. darkened color known as tarnish. The object of thisinvention is to provide silver alloys of fineness of sterling qualityand otherwise which possess tarnish-resisting properties and also whichmay be readily made into articles which possess sufficient hardness towithstand the usual wear and tear.

The invention comprises the novel compositions and component mixturescomprised insuch compositions, specific embodiments of which aredescribed hereinafter by way of example only and in accordance with whatI now consider the preferred manner of practicing the invention.

' The invention comprises a tarnish-resisting silver alloy containingsilver and tin and at least one other metal selected from a groupconsisting of cadmium, zinc, antimony, nickel-chromiiun alloy, copper,manganese, lithium, calcium and silicon. It includes alloys containingthe tollowing proportions:-about 85-93% silver and small amounts oflithium, calcium or silicon or mixtures thereof and the balance tin. Italso includes a melt mixture containing about 85-93% silver, plus about1 to 4% of cadmium, copper, zinc, antimony, manganese andnickel-chromium alloy and the balance tin. It also includes a meltmixture containing about 85-93% about 1 to 4% of cadmium, copper,'zinc,antlmony, and small amounts of lithium, calcium or silicon or mixturesthereof, and the balance tin. The amount'of lithium, calciurnor siliconused s preferably such that up to about 0.7% of one or more of thesemetals is found in the resulting finished alloy. The proportions oflithium, silicon and calcium or mixtures thereof mentioned may exceed0.7% if desirechbut in that case the resulting alloy is apt to bebrittle although it still possesses the desired tarnish-resistingproperties. A certain amount of these metalslithium, calcium, siliconlsapt to be lost in melting depending on the technique employed in theiraddition and it is therefore well to add a somewhat larger amountthereof to the mixed melt than expected in the resulting alloy asstated, this additional'amount will depend on the technique employed andcan be readily determined for a given case by making one or more meltsand silver plus.

observing the resulting amount of such metal obtained in the finishedmelt. The percentage of copper employed in making any of the abovealloys should preferably not exceed about 3.6%. In preparing the abovealloys it is important that on they be substantially homogeneousthroughout. The proportions just given produce homogeneous solid alloys.Heterogeneous combinations do not possess the desired properties and Ithere= fore have selected the homogeneous composit o5, tions given. Asregards the specific efiect of the metals present in the silver alloys,the properties were determined by testing a series of the alloys. Tinforms solid solution alloys with silver up to 15% tin and silver. Tinincreases the hard- 70 nesd'and lowers the melting point of theresulting alloy. Other elements as specified above imparttarnish-resisting properties to the silvertin alloy, and also increasethe hardness of the resulting alloy. Q 35 The results of the testsdemonstrated that the silver-tin alloys are more tarnish-resisting thanthe silver-zinc and the silver-antimony alloys. The inclusion of smallamounts of lithium, calcium, silicon, cadmium, zinc, antimony,manganese, copper, or nickel-chromium alloy in silvertin alloysincreases their tarnish-resisting properties. .Lithium, silicon andcalcium added to alloys of silver-tin with small amounts. of cad= mium,zinc, antimony and copper further increase the tarnlsh-resistingproperties.

Cadmium, zinc, antimony, copper, manganese and nickel-chromium alloyadded to silver-tin alloys control the workability oi the resultingalloys.

The compositions made up embodying the metals indicated above weretested to determine their tarnish-resisting properties as follows:Asmall'cast block of the composition to be tested was highly polished andcovered by a water solution of ammonium sulfide containing an excess offree sulfur. This solution of ammonium sulfide and sulfur was selectedfrom a number of tarnish-producing materials, as the most active of thevarious agents tested. The most satmo isfactory solution of ammoniumsulfide and free sulfur consisted of an N/lO- ammonium sulfide plusN/lOO excess free sulfur. The expressions N/ 10 and vN/lml are intendedto designate respectively 10th normal and th normal solutions. Inaccordance with the standard practive a normal solution is onecontaining an equivalent weight in grams of the substance dissolved inone liter of water or other solvent. The specimen was kept in contactwith this solution for nish was then observed on the specimen. Whenidentical specimens were exposed to the atmosphere for several months,the tarnish-resisting effects observed correspondedt to those obtainedin the much shorter interval required by the which are less or greaterthan sterling silver.

I give below a series of alloys prepared in accordance with myinvention, together with the results of the above tarnish test and theBrinnell hardness test made on the alloy as cast.

, I aplo Composition of mixtures melted-parts by weight 1 cadmium 0.5lithium cadmium, l lithium- .8 cadmium, 0.7 lithium 1.5 cadmium, 0.75calcium- .75 cadmium, 0.75 calcium .5 cadmium, l s1licon .7 cadmium, 1silicon. cadmium, 1.5 silicon .5 antimony. .6 antimony antimony, 0.5lithium.-- .5 antimony, 0.5 calcium--- .25 antimony, 0.75 calcium 3antimony, 0.5 calcium .6 antimony, 1 silicon copper pper .5 copper, 0.5lith|um 2.8 copper, 0.7 lithium.-- .5 copper, 0.5 calcium Proanalsilver, 6.

90 silver, 6.

seesssssssssssssssssssssssssssscswsaawss As is well understood inmelting volatile metals such as-cadmium and zinc there may be someoxidation and loss thereof. In making alloys therefrom such loss shouldbe compensated in the melt mixture if recovery of the proportions ofthose metals therein stated is to be made.

The alloys prepared as indicated in the above examples all showed byappropriate tests that they were substantially homogeneous alloys, be-

ing substantially free from heterogeneous struc- Each of the alloys ofthe above examples,

ture.

when subjected to the ammonium sulfide and sulfur tests indicated above,had a tarnish-resisting property capable of resisting such treatmentsubstantially without appearance of tarnish. Sterling silver andstandard silver and various other silver alloys when subjected to thistest. showed appreciable tarnish.

. rapidly oxidize.

-The silver em- 1,970,318 five minutes, then washed and dried. Thetarployed in the above melts was a fine commercial electrolytic silveras crystals of a high grade of purity and the other metals were alsocommercial products of high purity.

The following process is carried out in forming the alloys of the metalor metals with silver and tin:-

The alloys are prepared by melting the weighed amounts of electrolyticsilver and the other constituents under a flux of for example borax, orglass, and charcoal. The molten mixtures are thoroughly mixed, then castin the usual manner. When either lithium, calcium, or silicon is made aconstituent of the alloy, these metals may be added either as previouslyprepared alloys, or the silver alloy of lithium, calcium, or silicon mayfirst be prepared, and then thevother constituents added. It is foundthat lithium, calcium, and silicon can be easily incorporated withsilver by placing a layer of the electrolytic silver crystals in thecrucible, placing the lithium, calcium or the silicon on the layer ofsilver and covering with the remaining electrolytic silver. Thetemperature of the crucible is raised in the case of the lithium andcalcium to the melting point of the silver, bringing about the alloyingof the lithium and the calcium with the silver. If these metals wereadded to the molten silver or to the molten silver alloys, large lossesthereof would occur as oxidation occurs so readily. Due also to theirlow specific gravities as compared to silver, they float on the surfaceof the molten silver and Complete alloying of the required amounts ofeither lithium or calcium with the silver results according to the aboveprocess before the silver is completely melted. In the case of silicon,the combination, results when the silver is entirely melted.

The preparation of the 'alloys of tin with lith-'- ium or calcium can beperformed electrolytically,

thus producing a cheaper product than is possible by using the metallithium or calcium. The preparation oi the alloy of tin with lithium orcalcium is accomplished by electrolyzing a molten batch of the halogensalts of these latter metals using a carbon anode and molten tin as thecathode, which readily dissolves the lithium and calcium as rapidlyasthey are electrolytically liberated.

It will be observed herein described contain silver and tin, withsilthat the various alloys To this combination of silver and 'tin isadded one or more metals which alter the tarnish resistance of thesilver-tin combination and change as well the workability of theresulting alloy.

The other metals just referred to and which have ver rangingupwards fromapproximately 85%.

been previously set forth herein are:lithium,

calcium, silicon, cadmium, copper, zinc, antimony and nickel-chromium.

While I have described'my improvements in great detail and with respectto certain preferred embodiments thereof, I do not desire to be limitedto such details or embodiments since many changes and modifications maybe made and the invention embodied in widely different forms withoutdeparting from the spirit and scope thereof in its broader aspects.Hence I desire to cover all equivalents and all modifications and formscoming within the language or scope of any oneor more of the appendedclaims.

What I claim as new and desire to secure, by

Letters Patent, is:

.1. A homogeneous tarnish-resisting silver-tin holding in solid solutionas the remainder of thesalloycne or more workability-control metals,cadmium, zinc, antimony, nickel-chromium alloy, copper, manganese,lithium, calcium, selected in such amounts as will insure to theresulting alloy a Brinnell hardness of not less than 36, the aggregateamount of lithium and calcium not exceeding 1.0 per cent.

2. A tarnish-resisting silver alloy consisting of the following parts byweight silver about 85-93 per cent, tin about 3-14 per cent, less thanabout 1 per cent of a metal selected from the group lithium and calcium,and the remainder consisting of antimony and copper in appreciableamounts.

3. A tarnish-resisting silver alloy containing silver about 85-93 percent by weight, an ,appreeiable amount but less than 1 percent oflithium and 1-4 percent of a metal selected from the groupcadmium, zinc,antimony, nickelchromium alloy, manganese and tin constituting theremainder. r

4. A tarnish-resisting silver alloy consisting of the following parts byweight, silver about 90-91 per cent, tin about 6-8.5 perv cent, anappreciable amount but less than 1 per cent of calcium and the remainderconsisting of antimony.

5. A tarnish-resisting silver alloy containing about 85-93 per cent ofsilver by weight, a metal selected from the group lithium, calcium inthe proportion by weightof an appreciable amount but less than 1 percent, and tin constituting substantially the remainder of the alloy.

:ED'WARD F. KERN. I

CERTIFICATE 0t contention.

Patent No. i, 970, 31 8;

' August 14, 1934.

EDWARD r. KERN.

it is hereby certified that error apnears in the printed specificationof the above numbered patent requiring correction as follows:

Page 1, lines 106-107,-

tor the misspelled word ".practive" read practice; page 2, line '121,for "batch" read bath; and that the said Letters Patent should be readwith these corrections therein that the same may conform to the recordof the case in the Patent Office. Signed and sealed this 18th day .0:September, A. D. 1934.

(Seal) Leslie Frazer Acting Commissioner of "Patents,

holding in solid solution as the remainder of thesalloycne or moreworkability-control metals, cadmium, zinc, antimony, nickel-chromiumalloy, copper, manganese, lithium, calcium, selected in such amounts aswill insure to the resulting alloy a Brinnell hardness of not less than36, the aggregate amount of lithium and calcium not exceeding 1.0 percent.

2. A tarnish-resisting silver alloy consisting of the following parts byweight silver about 85-93 per cent, tin about 3-14 per cent, less thanabout 1 per cent of a metal selected from the group lithium and calcium,and the remainder consisting of antimony and copper in appreciableamounts.

3. A tarnish-resisting silver alloy containing silver about 85-93 percent by weight, an ,appreeiable amount but less than 1 percent oflithium and 1-4 percent of a metal selected from the groupcadmium, zinc,antimony, nickelchromium alloy, manganese and tin constituting theremainder. r

4. A tarnish-resisting silver alloy consisting of the following parts byweight, silver about 90-91 per cent, tin about 6-8.5 perv cent, anappreciable amount but less than 1 per cent of calcium and the remainderconsisting of antimony.

5. A tarnish-resisting silver alloy containing about 85-93 per cent ofsilver by weight, a metal selected from the group lithium, calcium inthe proportion by weightof an appreciable amount but less than 1 percent, and tin constituting substantially the remainder of the alloy.

:ED'WARD F. KERN. I

CERTIFICATE 0t contention.

Patent No. i, 970, 31 8;

' August 14, 1934.

EDWARD r. KERN.

it is hereby certified that error apnears in the printed specificationof the above numbered patent requiring correction as follows:

Page 1, lines 106-107,-

tor the misspelled word ".practive" read practice; page 2, line '121,for "batch" read bath; and that the said Letters Patent should be readwith these corrections therein that the same may conform to the recordof the case in the Patent Office. Signed and sealed this 18th day .0:September, A. D. 1934.

(Seal) Leslie Frazer Acting Commissioner of "Patents,

